1. Field of the Invention
The present invention concerns a method to determine a position shift of a focal area as well as a corresponding device. The invention in particular concerns such a method and device in the field of hyperthermia application.
2. Description of the Prior Art
Hyperthermic treatment of tumor tissue has attracted increasing interest in medical cancer treatment. In such a hyperthermic treatment of tumor tissue (also called hyperthermia) the tumor tissue is heated to temperatures of over 42.5° C. Hyperthermia in cancer treatment is frequently used as a measure supporting radiation and/or chemotherapy. Hyperthermic treatment of tumor cells in which these cells are heated to temperatures of, for example, above 60° C., is often referred to as heat therapy; such treatment generally leads to a heat-induced destruction of the tumor cells.
In hyperthermia, differentiation is made between whole-body hyperthermia and local hyperthermia. Whole-body hyperthermia can occasionally lead to severe stress on the cardiovascular system of the patient.
By contrast, local hyperthermia is intended to overheat only a narrowly defined region, for example only the tumor tissue. Ultrasonic waves, infrared rays, microwaves or laser beams which are normally focused on the area to be heated (thus the tumor tissue, for example) using a corresponding hyperthermia applicator in order to achieve an overheating (in particular a local overheating), whereby the tumor tissue is damaged or entirely destroyed by the overheating. This is also referred to as thermal ablation or thermoablation.
In order to guarantee the effectiveness of such a local treatment, and in order to avoid the destruction of healthy tissue, it is necessary to know the position of the tumor precisely in order to ensure the precise alignment of the focus of the hyperthermia applicator relative to the focal area to be heated in a subsequent treatment.
For this purpose, in DE 694 28 146 T2 an ultrasound device is disclosed in which a patient is placed on a treatment table of the device during a hyperthermia treatment so that the tumor to be heated is localized over a treatment opening located in the treatment table. An ultrasonic wave applicator is rigidly attached below the treatment opening, so the position of the ultrasonic wave applicator is fixed relative to the area to be heated. A shift of the ultrasonic wave focus relative to the area to be heated can nevertheless occur, for example as a result of a movement of the patient (for example a breathing movement), and therefore the risk of damage to healthy tissue cannot be entirely precluded.